Display Device Uniforming Light Distribution Throughout Areas and Method for Manufacturing Same

ABSTRACT

Disclosed arm an optical display device producing uniform light distribution and a method of fabricating such devices. The optical display device has waveguides arranged in vertical and horizontal directions. The waveguide has a conical shape whose cross-section decreases towards the light-projection side thereof. At least one of the size, height, spacing, and refraction index of the waveguide is designed to be different for each section, depending on an incident angle and/or intensity of light inputted from a light source. Therefore, the intensity of projected light can be made uniform over all sections of the optical device.

TECHNICAL FIELD

The present invention relates to an optical display device producing auniform light distribution over the entire area. More specifically, theinvention relates to such devices and a method of fabricating the same,in which the size, the height, the spacing, and the refraction index ofwaveguides are all designed to be different for each section, dependingon an incident angle and/or light intensity inputted from a lightsource, and thus a uniform light distribution can be achieved over thewhole area of the optical device while maintaining a desired viewingangle, and the luminance in the peripheral area of the device can beavoided from being degraded.

BACKGROUND ART

In general, a projection device such as a projection TV, a projectionmonitor, or the like is equipped with a rear projection screenprojecting images toward the viewer's side. This rear projection screenis one of the optical display devices designed such that the imagesprojected from the rear side of the screen pass through a viewing space.The viewing space may be relatively large (for example, a projectionTV), or may be relatively small (for example, a projection monitor). Theperformance of a rear projection screen can be described by variouscharacteristics of the screen. The screen performance typically includesgain, viewing angle, resolution, contrast ratio, color, and undesirableartifacts such as specks. The rear projection screen needs to have ahigh resolution, a high contrast ratio, and a high gain.

In addition, it is preferable that the rear projection television has awide viewing angle capable of covering all the viewers within a broadrange of angle. In order to achieve this wide viewing angle, the screenis provided with waveguides thereinside. In a rear projection screen,inherently, a point light source is positioned rearwards of the screencenter and thus the incident angles of the light are different in thecentral area and the peripheral area of the screen. If the entire screenis formed of waveguides of the same structure, the reflection anglesinside the waveguides are different from one section of the screen toanother, due to their different incident angles. Some waveguides may notexperience total reflection, depending on the position thereof. Usually,the waveguides, specially designed for a wide viewing angle, come to beplaced in the central area of the screen. Therefore, in a case where thescreen is designed with identically structured waveguides, the intendedwide viewing angle can be achieved on the whole since the peripheralarea of the screen is provided with the same waveguides. However, theluminance in the peripheral area is considerably degraded relative tothe central area of the screen. For this reason, the imagedistinctiveness and clarity are made different in the central andperipheral areas of the screen, and homogeneity in the image isconsequently degraded, thereby failing to achieve a high quality image.

In particular, a large-scale display device employs a plurality of unitlight sources or a single diffusive light source, and the lightintensity thus becomes non-uniform throughout the screen. Morespecifically, in the case where a plurality of light sources is used,the light intensity is lowered in the boundary area between the lightsources. When a single diffusion light source is employed, the centraland peripheral areas of the screen exhibit different luminance, due todifferent incident angles and different light-paths. For the abovereasons, the brightness is not uniform over the entire screen,consequently resulting in non-uniform image distinctiveness and clarity,and degraded image resolution.

DISCLOSURE OF INVENTION Technical Problem

Accordingly, the present invention has been made in order to solve theabove problems in the prior art. It is an object of the invention toprovide an optical display device producing a uniform lightdistribution, in which the sidewall gradient of waveguides is designedto be different in the central and peripheral areas of a screen in sucha way as to be gradually decreased radially away from the central areatowards the peripheral area, thereby preventing degradation in theperipheral luminance.

Another object of the invention is to provide an optical display deviceproducing a uniform light distribution, in which the sidewall gradientof waveguides is gradually decreased from the central area of a screenin a horizontal or vertical direction towards the peripheral area,thereby achieving a uniform luminance over the entire screen.

A further object of the invention is to provide a method of fabricatingsuch optical display devices, in which ultraviolet-exposing time varieswith each section of a screen using a line-scanning mode, therebyenabling the formation of waveguides having a sidewall gradientgradually decreasing toward the peripheral area from the central area.

A further object of the invention is to provide an optical displaydevice producing a uniform light distribution, in which the size, theheight, the spacing, and the refraction index of waveguides is designedto be different for each section, depending on incident angle and/orintensity of light inputted from a light source, thereby achieving auniform light distribution over the whole area of the optical device.

A further object of the invention is to provide an optical displaydevice, in which the line spacing of a photomask is set up to bedifferent, depending on incident angle and/or intensity of a lightinputted from a light source, thereby achieving a uniform lightdistribution over the whole area of the optical device.

Technical Solution

In order to accomplish the above objects, according to one aspect of theinvention, there is provided an optical display device producing auniform light distribution, the optical display device includingwaveguides each having a sidewall inclined from the bottom side thereof,imaging light rays incident from a light source placed rearwards of thecenter of the optical device being reflected inside the waveguide to beprojected to the outside of the waveguide, wherein the waveguidesarranged over the whole section of a screen have a same bottom side anda same height, and simultaneously the sidewall gradient in thewaveguides is decreased gradually, within an angle range within which atotal reflection occurs, towards the peripheral area of the screen fromthe central area thereof, such that the imaging light rays are lessfrequently reflected in the waveguide in the peripheral area of thescreen, as compared with the waveguides in the central area of thescreen.

According to another aspect of the invention, there is provided anoptical display device producing a uniform light distribution, theoptical display device including waveguides each having a sidewallinclined from the bottom side thereof, imaging light rays incident froma light source placed rearwards of the center of the optical devicebeing reflected inside the waveguide to be projected to the outside ofthe waveguide, wherein the waveguides arranged over the whole section ofa screen have a same bottom side and a same height, and simultaneouslythe sidewall gradient in the waveguides is decreased gradually, withinan angle range within which a total reflection occurs, towards theradially peripheral area of the screen from the central area thereof,depending on the incident angle, such that the waveguides at a radiallysame distance from the central area have a same sidewall gradient insymmetrical fashion with respect to the central area.

According to yet another aspect of the invention, there is provided anoptical display device producing a uniform light distribution, theoptical display device including waveguides each having a sidewallinclined from the bottom side thereof, imaging light rays incident froma light source placed rearwards of the center of the optical devicebeing reflected inside the waveguide to be projected to the outside ofthe waveguide, wherein the waveguides arranged over the whole section ofa screen have a same bottom side and a same height, and the sidewallgradient in the waveguides is gradually decreased simultaneously withinan angle range within which a total reflection occurs, along either ahorizontal direction or a vertical direction, towards the peripheralarea of the screen from the central area thereof, depending on theincident angle.

According to a further aspect of the invention, there is provided amethod of fabricating the above-described optical display device. Themethod comprises: a first step of placing a grid on a photomask andattaching a transparent substrate on the grid; a second step of coatinga photopolymer material on the transparent substrate; a third step ofradiating ultraviolet rays in a line-scanning mode on the photopolymermaterial from below the photomask the exposure time of the ultravioletrays being controlled for each section of a screen so as to formwaveguides having a sidewall gradient decreasing gradually towards theperipheral area along one direction from the central area of the screen;and a fourth step of attaching a front transparent plate on thewaveguides.

According to a further aspect of the invention, there is provided anoptical display device producing a uniform light distribution, theoptical display device having waveguides arranged in vertical andhorizontal directions, the waveguide having a conical se whosecross-section decreases towards the light-projection side thereof,wherein at least one of the size, height, spacing, and refraction indexof the waveguide is designed to be different for each section, dependingon incident angle and/or intensity of a light inputted form a lightsource such that the intensity of projected light can be made uniformover the entire section of the optical device.

According to a further aspect of the invention, there is provided anoptical display device producing a uniform light distribution, theoptical display device having waveguides arranged in vertical andhorizontal directions, the waveguide having a conical shape whosecross-section decreases towards the light-projection side thereof,wherein the size of the waveguide is designed to be different for eachsection, depending on incident angle and/or intensity of light inputtedfrom a light source such that the intensity of projected light can bemade uniform over the entire section of the optical device.

According to a further aspect of the invention, there is provided anoptical display device producing a uniform light distribution, theoptical display device having waveguides arranged in vertical andhorizontal directions, the waveguide having a conical shape whosecross-section decreases towards the light-projection side thereof,wherein the refraction index of the waveguide is designed to bedifferent for each section, depending on incident angle and/or intensityof light inputted from a light source such that the intensity ofprojected light can be made uniform over the entire section of theoptical device.

According to a further aspect of the invention, there is provided amethod of fabricating an optical display device, the optic displaydevice having different-sized waveguides for different sections. Themethod comprises the steps of: attaching a photopolymer on a photomaskhaving a grid structure whose line spacing is non-uniform, radiatingultraviolet rays on the photopolymer from outside of the photomask suchthat waveguides having different sizes are formed in the photopolymerdue to the non-uniform line spacing of the grid structure of thephotomask; removing the photopolymer excepting the formed waveguideportions through a development process; and filling a resin having a lowrefraction index in a valley-like space between the waveguides formedthrough the development process.

ADVANTAGEOUS EFFECTS

As described above, in the present invention, the sidewall gradient ofwaveguides is designed to be different in the central and peripheralareas of a screen in such a way as to be gradually decreased radiallyaway from the central area towards the peripheral area. Thus,degradation in the peripheral luminance can be avoided. In addition, thesidewall gradient of waveguides is gradually decreased from the centralarea of a screen in a horizontal or vertical direction towards theperipheral area, thereby achieving uniform luminance over the entirescreen.

Furthermore, the size, height, spacing, and refraction index ofwaveguides are designed to be different for each section, depending onincident angle and/or intensity of light inputted from a light source.Therefore, a uniform light distribution can be achieved over the wholearea of the optical device, and homogeneity in the projected image canbe consequently enhanced.

In addition, a low index resin is filled in the valley-like spacebetween the waveguides and a light diffuser is added to the low indexregion, thereby further improving the uniform light distribution. Here,the mated particle size, and contents of the light diffuser can becontrolled to adjust the light distribution.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects and advantages of the invention can be more fullyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings in which:

FIGS. 1 to 4 are schematic diagrams showing the reflection of imaginglight rays inside different waveguides having different designs;

FIG. 5 is a sectional view of an optical display device producing auniform light distribution according to a first embodiment of theinvention, where the invention is applied to a projection screen;

FIGS. 6 to 8 show one example for the configuration of the waveguides inthe optical display device in FIG. 5;

FIGS. 9 to 11 illustrate another embodiment of the waveguide structurein the optical display device in FIG. 5;

FIG. 12 is a process diagram explaining a method of fabricating theoptical display device illustrated in FIGS. 9 to 11;

FIG. 13 is a schematic diagram showing the variation of the sidewallgradient with the light-exposing time;

FIGS. 14 and 15 are a front and rear perspective view of an opticaldisplay device producing a uniform light distribution according to asecond embodiment of the invention;

FIG. 16 is a sectional view taken along the line E-E in FIG. 14;

FIG. 17 is a partial sectional view of a modified example of FIG. 16;

FIG. 18 is a process diagram explaining a method of fabricating theoptical device according to the second embodiment of the invention,which is illustrated in FIGS. 14 to 16;

FIG. 19 is a plan view showing the grid structure of a photomask used inthe manufacturing process of FIG. 18;

FIG. 20 shows a display panel such as an La) or an LED;

FIG. 21 is a graph showing the luminance for every section of thedisplay panel of FIG. 20;

FIG. 22 illustrates a display panel having an optical device of theinvention mounted thereon;

FIG. 23 is a graph showing the luminance for every section of thedisplay panel of FIG. 22;

FIG. 24 shows a conventional optical device using a plurality of unitlight sources;

FIG. 25 shows an optical device of the invention using a plurality ofunit light sources;

FIG. 26 depicts a conventional display device using a single diffusionlight source;

FIG. 27 illustrates an optical display device of the invention using asingle light source;

FIG. 28 is a graph contrasting the light characteristics of the opticaldevice of the invention in FIG. 21 with the conventional one of FIG. 20;

FIGS. 29 and 30 are a front and rear perspective view of an opticaldisplay device producing a uniform light distribution according to atint embodiment of the invention;

FIG. 31 is a sectional view taken along the line F-P in FIG. 29;

FIG. 32 is a partial sectional view of another embodiment modified fromthat of FIG. 31;

FIG. 33 is a process diagram explaining a method of fabricating anoptical device according to the third embodiment of the invention andillustrated in FIGS. 29 to 31;

FIG. 34 is a partial sectional view of an optical display deviceproducing a uniform light distribution according to a fourth embodimentof the invention;

FIGS. 35 and 36 explains a method of fabricating the optical displaydevice of FIG. 34; and

FIGS. 37 and 38 illustrate modifications for the fourth embodiment ofthe invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The preferred embodiments of the present invention will be hereafterdescribed in detail with reference to the accompanying drawings. Theembodiments of the invention will be explained, illustrating aprojection screen.

FIGS. 1 to 4 are schematic diagrams showing the reflection of imaginglight rays inside different waveguides having different designs.

Referring to FIGS. 1 and 2, the principles for a waveguide design inorder to obtain uniform luminance will be explained. FIGS. 1 and 2 arediagrams showing the reflection of imaging light rays inside awaveguide, where the length of its bottom face is 40 nm and the gradientof its sidewall is 10.52° Specifically, FIG. 1 shows the reflection ofimaging light rays in the case of an incident angle of zero degree (0°and FIG. 2 is in a case of 10 of incident angle. Here, the incidentangle is measured with respect to the normal line to the light inputsurface of the waveguide.

In addition to the length of the bottom face and the gradient of thesidewall, the refection index of the waveguide is 1.6, the refractionindex of the projection surface is 1, the critical angle for totalreflection inside the waveguide is 54.35° and the critical angle fortotal reflection on the projection surface (*e tip of the waveguide) is38.68° Typically, a point light source is positioned rearwards of thescreen center, and thus a waveguide placed in the screen center has anincident angle q₁ of zero degree (0°), as in FIG. 1. The imaging lightrays L₁ are reflected on the sidewall S₁ of the waveguide. With thisincident angle q₁, the imaging light rays perform a total reflectionuntil the second reflection. The second-reflected imaging light rays L₁again reach the sidewall S₁ at the height of approximately 83 mm, asillustrated in FIG. 1. In order to achieve a wide viewing angle,commonly, at least one or two reflections are needed, and in order toobtain a high luminance, a total reflection is required. Thus, in thecentral area of the screen, the length of the waveguide needs to bedetermined to be no more than a height corresponding to three times thatof the reflections to thereby meet the above conditions. As thefrequency of total reflections increases, the viewing angle is widened.Preferably, the height of the waveguide is determined to be within arange of from 73 mm (second reflection) to 83 mm (third reflection).

On the other hand, since the point light source is placed rearwards ofthe screen center, in the outer peripheral area of a screen, the imaginglight rays L₂ are incident at a certain angle, not vertically, as shownin FIG. 2. In the case where the incident angle q₂ is 10° the imaginglight rays perform a total reflection on the sidewall S1 at the time offirst reflection only. At this time, as depicted in FIG. 2, the heightof the waveguide needs to be determined to be no more than about 51 mmin order to obtain a high luminance. This is because, if a totalreflection does not occur inside a waveguide, light loss is causedinside the waveguide, degrading the luminance.

In view of the above explanation in conjunction with FIGS. 1 and 2, ifit is assumed that a waveguide has the same length of bottom face andthe same gradient of sidewall, waveguides in the central area of thescreen need to be designed to have a height of 73˜83 mm. In contrast, itis preferable that the waveguide in the peripheral area of the screen isdesigned to have a height within 50 mm. Thus, if this consideration isreflected upon the design of a waveguide, the screen becomes higher inits central area and lower in its outer peripheral areas and thus thescreen cannot have a uniform height. Consequently, overall, the screenhas an even surface, which is not preferable in terms of the viewingangle and the resolution thereof, and which also leads to a complicatedmanufacturing process.

In addition, FIGS. 3 and 4 are schematic diagrams showing the reflectionof imaging light rays inside a waveguide, the length of whose bottomface is 40 mm and the gradient of whose sidewall is 7° Morespecifically, FIG. 3 shows the relationship between the g light rays andthe waveguide structure in the case where the incident angle is zerodegrees (0°), and FIG. 4 is a case where the incident angle is tendegrees (10°).

The refraction index, the critical angle for total reflection, and thelength of the bottom face are the same as in both FIGS. 1 and 2, and thegradient of the sidewall (7°) is different from the previousillustration of FIGS. 1 and 2. In the case where the incident angle q₃is 0° as shown in FIG. 3, the incident imaging light rays L₃ are totallyreflected on the sidewall S₂ until the third reflection. At is time,total reflection occurs within the height of 137 mm.

On the other hand, when the incident angle q₄ is 10 degrees (°), theimaging light rays L4 perform a total reflection until secondreflection, as shown in FIG. 4. The maximum height of the waveguide,within which total reflection occurs, is 96 mm, and thus the height ofthe waveguide needs to be determined to be no more than 96 mm in orderto obtain a high luminance.

In view of the above explanation in conjunction with FIGS. 3 and 4, ifthe height of the waveguide is designed so as to be suitable for theperipheral waveguides where the incident angle is 7 degrees (°), thecentral waveguides in the screen experience only one total reflection,thus failing to achieve an effective viewing angle. Generally, it ispreferable that the screen is configured such that its central area hasa wider viewing angle. Therefore, it is preferable that the centralwaveguides are designed so as to cause at least two ties of totalreflections.

Considering the above two cases where the gradient of sidewall is 10.52°(FIGS. 1 and 2) and 7° (FIGS. 3 and 4), an optimum condition for totalreflection can be determine over the entire area of a screen. Forexample, the height of the waveguide is established to be 80 mm, whichis within a common height range where a total reflection can occur inboth the central and the peripheral area of the screen. Simultaneously,the gradient of the waveguide is determined to be 10.52° for the centralarea of the screen and 7° for the peripheral area of the screen. Morespecifically, the central waveguides of the screen are configured suchthat the sidewall thereof has a gradient of 10.52° as illustrated inFIGS. 1 and 2. The peripheral waveguides of the screen are structured soas to have a gradient of 7° as illustrated in FIGS. 3 and 4. In thisway, one or two times of total reflections can occur in all thewaveguides arranged over the whole screen, and thus a wide viewing anglecan be achieved in the central area thereof and a high luminance can beobtained in the peripheral area thereof. Here, the sidewall gradients ofthe waveguides are designed so as to decrease gradually towards theperipheral waveguides from the central ones in the screen. That is, thesidewall gradient is decreased gradually by a certain increment of angletowards the outer waveguides within the range of 10.52˜7° over theentire screen. Thus, the sidewall gradient may decrease towards theouter peripheral waveguides in a symmetrical pattern about the screencenter or in a non-symmetrical fashion. As one exemplary approach, thesidewall gradient may be gradually decreased in a concentric pattern insuch a way that the same magnitude of gradient is provided to thewaveguides placed at the same distance from the central waveguide. Inthis case, the sidewall gradient decreases gradually in radial directiontowards the outer periphery of the screen from the center thereof, thusachieving a uniform luminance in vertical and horizontal directions,i.e., along the radial directions. An exemplary screen according to thisembodiment is illustrated in FIGS. 6 to 8.

As an alternative, the sidewall gradient may be decreased graduallytowards the peripheral ara of the screen along the horizontal orvertical direction from the horizontal center of the screen or from thevertical cent thereof. In this case, the gradual decrease of thegradient is applied to either one of the horizontal and verticaldirections, and thus the luminance can be improved along any onedirection only. However, even if the luminance is improved along any onedirection so as to be suitable to its use, a common screen or monitor isenabled to provide a distinct and clear image. This will be hereinafterexplained in detail, in conjunction with FIGS. 9 to 11.

FIG. 5 is a sectional view of an optical display device producing auniform light distribution according to a first embodiment of theinvention, where the invention is applied to a projection screen. InFIG. 5, the projection screen of the invention is generally denoted at1. FIGS. 6 to 8 show one example for the configuration of the waveguidesin the optical display device in FIG. 5. FIG. 6 is a perspective view ofthe waveguide array, FIG. 7 is a sectional view taken along the line A-Ain FIG. 6, and FIG. 8 is a sectional view taken along the line B-B inFIG. 6.

As illustrated in FIG. 5, the projection screen 1 of this embodimentincludes a front transparent plate 10, a rear transparent substrate 20,and a waveguide array 30 interposed in-between. A unit waveguide 32(hereinafter, referred to as a “waveguide”) is structured to have asmaller bottom face to a light source 40 side and a larger top facecontacted with the front transparent plate 10. That is, the waveguide 32is structured such that its cross-section is gradually narrowed towardsthe front side of the screen, to which imaging light rays L areprojected. Thus, the waveguides 32 have an inclined sidewall, andconsequently may have the she of a conical frustum or a polypyramidalfrustum. In this embodiment, the waveguide is illustrated to have apyramidal frustum. Between the waveguides 32 is formed a space, in whicha light-absorbing material 34 is filled. The light-absorbing material 34absorbs light rays incident from the outside of the screen so that theimaging light projected from the inside can be viewed more clearly anddistinctly. The light absorbing material 34 is formed of a mixture of amonarch-carbon black, a baysilone-platinum catalyst, and a vinylsilicone material.

As depicted in FIG. 6, in the waveguide array 30, a horizontalcenterline C_(H) and a vertical centerline C_(V) intersect at the centerpoint C_(P). The waveguides at the same distance from the center pointC_(P) have the same sidewall gradient A_(S). At the same time, thesidewall gradient A_(S) of the waveguide 32 is decreased graduallytowards the outer peripheral area of the screen 1 from the center pointC thereof. Thus, the sidewall gradient A_(S) of the waveguide 32gradually decreases in a concentric pattern toward the outer part of thescreen 1 from the center thereof. When sectioned along an arbitrary linepassing through the center point C_(P), the screen 1 has a left-rightsymmetrical structure, in particular, in terms of the sidewall gradientof the waveguides. At this time, the concentric pattern may include acircular concentric pattern and an oval-concentric pattern. A circularconcentric pattern is more efficient. For example, in the cross-sectionof the waveguide array 30 taken along the horizontal centerline as shownin FIG. 7, the sidewall gradient A_(S1) of the waveguides is formed in aleft-right symmetrical fashion about the center point C_(P). As shown inFIG. 8, in the cross-section of the waveguide array 30 taken along thevertical centerline of the screen 1, the sidewall gradient A_(S2) of thewaveguides 32 is formed in a up-down symmetrical fashion about thecenter point C_(P).

The sidewall gradient A of the waveguide 32 is defined with respect tothe normal ha to the light input surface of the waveguide as follows.

A _(S)=tan⁻¹((h−t)/X), h=H/2, t=T/2.

Here, H denotes the length of the bottom side, T denotes the length ofthe topside, and X is the height of the waveguide in the verticalcross-section of the waveguide.

The waveguides placed in the central area of the screen are preferred tohave a sidewall gradient of 10˜12° and the waveguides placed in theoutermost area thereof are preferred to have a sidewall gradient of 6˜8°In addition, preferably, the pitch, which is the spacing between thebottom sides of the waveguides, is determined to be less than 3 mm.

In addition, the refraction index of the waveguide 32 is 1.4˜1.6, therefraction index of the light projection surface is 1.0˜1.2, and therefraction index of the light-absorbing material 34 is 1.2˜1.3. When adiffusion plate is applied to the front face of the waveguide 32, therefraction index of the waveguide 32, the light projection surface, andthe light-absorbing material 34 are preferred to be 1.6, 1.0, and 1.2respectively. If the diffusion plate is not employed, the refractionindex of the waveguide 32, the light projection surface, and thelight-absorbing material 34 are preferred to be 1.6, 1.1, and 1.2respectively.

In this case, the critical angle for total reflection inside thewaveguide is 45˜50° and the critical angle for total reflection on thelight projection she is 35˜60° For example, if a diffusion plate isemployed, the critical angle for total reflection inside the waveguideis preferred to be 45˜50° and the critical angle for total reflection onthe light projection surface is preferred to the 40˜45° In addition,when the diffusion plate is not employed, the critical angle for totalreflection inside the waveguide is preferred to be 45˜50° and thecritical angle for total reflection on the light projection surface ispreferred to be 35˜40°

Consequently, over the entire screen 1, each waveguide 32 has the samelength H of the bottom side and the same height X. Due to the variationin the sidewall gradient A_(S), the length T of the topside varies withthe waveguides. Here, it is preferable that the sidewall gradient A_(S)between the adjacent waveguides is varied within 2%, the topside betweenthe adjacent waveguides is varied within 5%.

The waveguides placed in the central area of the screen 1 have thehighest sidewall gradient A_(S) and thus the incident image light raysare outputted after being totally reflected several times, at least twoor more times, thereby resulting in a wider viewing angle. In contrast,the sidewall gradient A_(S) of the waveguide 32 is gradually dec towardsthe peripheral area of the screen. Accordingly, for the waveguidesplaced in the outer peripheral area, hex total reflection of imaginglight is less frequent. Therefore, the peripheral area of the screen 1has a relatively narrower viewing angle due to less frequent totalreflections, but remains within the allowed frequency of totalreflection, thereby minimizing the light loss and thus preventingdegradation in luminance.

MODE FOR THE INVENTION

FIGS. 9 to 11 illustrate another embodiment of the waveguide structurein the optical display device in FIG. 5. FIG. 9 is a perspective view ofthe waveguide array, which is denoted by reference numeral 60, FIG. 10is a sectional view ten along the line C-C in FIG. 9, and FIG. 11 is asectional view taken along the line D-D in FIG. 9.

As illustrated in FIGS. 9 and 10, the waveguide array 60 of thisembodiment is designed such that the sidewall gradient A_(S) of thewaveguide 62 is gradually decreased towards the peripheral area of thescreen in a horizontal direction from the vertical centerline C_(V).That is, the sidewall gradient A_(S) varies in a left-right symmetricalfashion about the vertical centerline C_(V). For example, the sidewallgradient of the waveguide 62 placed in the center is 10.52° theoutermost waveguide has a sidewall gradient of 7° and the sidewallgradients of the waveguides in-between are gradually decreased withinthe range of 10.52˜7° On the other hand, all (the waveguides along thevertical direction have the same sidewall gradient. In this embodiment,the sidewall gradient of waveguide is decreased gradually along thehorizontal direction from the vertical centerline, but remains constantalong the vertical direction. However, the opposite case, i.e., the casewhere the waveguide array 60 is rotated by 90 degrees (°), is includedin the embodiments of the invention. Therefore, in this embodiment, thesidewall gradient decreases in a symmetrical pattern with respect toeither the horizontal centerline or the vertical centerline, thusenhancing the luminance of the peripheral area of the screen.

FIG. 12 is a process diagram explaining a method of fabricating theoptical display device illustrated in FIGS. 9 to 11. FIG. 13 is aschematic diagram showing the variation of the sidewall gradient withthe light-exposing time.

The method of fabricating a screen 3, in which the sidewall gradient ofthe waveguides is decreased gradually along one direction, will bedescribed, referring to FIG. 12. First, a grid 72 is placed on thephotomask 70 and a transparent substrate 80 is attached on top of thegrid 72 (step S₁, S₃). Then, due to the grid 72, a gap is formed betweenthe photomask 70 and the transparent substrate 80. In order to removethe gap, a filling material 82 is filled in the gap. The fillingmaterial may employ a high-purity isopropanol alcohol (IPA). Thetransparent substrate 80 may be formed of a transparent resin such aspolyethylene terephthalate (PET), polymethyl methacrylate (PMMA), ormethyl methacrylate styrene (MS) copolymer.

Thereafter, a photopolymerizable material 90 is coated on thetransparent substrate 80 (step S₅). The photopolymerizable material 90may be formed by mixing two or more materials selected from etyoxylated(3) bisphenol A diacrylate, trimethylolptopane lolptopane triacrylate,irgacure, irganox, and the like. Preferably, the photopolymerizablematerial 90 may be formed by mixing all the above four materials, morespecifically, 40˜80 wt % of diacrylate, 0.5˜10 wt % of triacrylate,0.5˜12 wt % of irgacure, and 0.5˜12 wt % of irganox. Here, diacrylate isan ultraviolet polymerizable monomer, triacrylate is a monomer foradjusting viscosity, irgacure is an ultraviolet polymerizationinitiator, and irganox is an inhibitor against oxide formation.

Next, ultraviolet rays are radiated to form a waveguide 62 shape in thephotopolymerizable material 90 (step S₇). When radiating the ultravioletrays, a line scanning method is used to control the exposing time foreach section and thus forms a waveguide 62 having different sidewallgradients for different sections. As shown in FIG. 13, as the lightexposure time is extended, the sidewall gradient A_(S) of the waveguide62 is decreased. On the contrary, as the light exposure time isshortened, the sidewall gradient A_(S) of the waveguide 62 is increased.Thus, according to this principle, when performing the line scanning,the exposure time is decreased gradually towards the central area fromone horizontal end of the substrate such that the center point thereofhas the minimum exposure time. After passing the center point, theexposure time is gradually increased towards the other horizontal end ofthe substrate. Thus, the sidewall gradients of de waveguides aredistributed in a left-right symmetrical pattern in such a way as to bedecreased towards both the left and right ends of the substrate from thecenter point.

Excepting the waveguide 62 shape formed through the UV exposure, theunexposed portion is developed and removed (step S₉). Then, a space isformed between the waveguides. A light-absorbing material 64 is filledin the space 63 and a front transparent plate 100 is then attached, thuscompleting the projection screen 3 of the invention (step S₁₁). Thefront transparent plate 100 may be made of the same material as thetransparent substrate 80.

The operation and effects of the invention will be described in greaterdetail, referring to FIG. 5.

The light rays emitted from the light source 40 are converted intoimaging light rays containing images. Then, the imaging light rays areconverted into substantially parallel light rays through a Fresnel lens42 and incident on the screen 1. Thus, the imaging light rays passthrough the rear transparent substrate 20 and are inputted into thewaveguide 32. While passing through the waveguide, the light rays arereflected on the sidewall and projected towards the front of the screenso as be seen by a viewer. At this time, since the waveguides in thecentral area of the screen 1 have a larger sidewall gradient, the lightreflection occurs relatively frequently. The incident angle in thecentral area is zero degree (0°), and thus the imaging light rays areoutputted after two or three times of total reflections inside thewaveguide to thereby widen the viewing angle thereof. In contrast in theperipheral area of the screen, the waveguides 32 have a relativelysmaller sidewall gradient, the incident imaging light rays are lessfrequently reflected inside the waveguide before being outputted.Therefore, in the outer peripheral area of the screen, the light losscaused through reflection can be maximally suppressed such that theperipheral luminance is almost the same as it is in the central area. Inthis way, according to the present invention, the sidewall gradient ofthe waveguides 32 is adjusted to a suitable value for every section ofthe screen to thereby achieve quality images in terms of the viewingangle and luminance thereof.

FIG. 5 illustrates only the central and peripheral waveguides 32, butthe screen contains numerous waveguides in-between. The areas betweenthe waveguides are filled with a light-absorbing material 34 forabsorbing external lights incident into the screen 1, thereby improvingthe distinctiveness and clarity of the imaging light rays projected fromthe inside. A diffuser may be applied to the front transparent plate 10.

FIGS. 14 and 15 are a front and rear perspective view of an opticaldisplay device producing a uniform light distribution according to asecond embodiment of the invention. FIG. 16 is a sectional view takenalong the line D-E in FIG. 14, and FIG. 17 is a partial sectional viewof a modified example of FIG. 16. In this embodiment, the waveguideshave a uniform height. In addition, the optical device according to theinvention may or may not be provided with a transparent protection plateattached to the front face or the rear face thereof. The followingembodiments illustrate cases having no transparent protection plateattached thereto, and are referred to as an “optical device.”

In the optical display device 110 of this embodiment, the waveguide 112has a truncated conical shape whose cross-sectional area graduallydecreases towards the light output surface thereof. These waveguides arearranged in vertical and horizontal directions. In particular, theheight of the waveguide 112 is uniform over the whole region of theoptical device 110, but the size thereof varies over the entire area ofthe device. That is, as shown in FIG. 16, the size of the waveguides 112a to 112 f increases gradually towards the peripheral area of theoptical device 110 from the central area thereof, mom precisely, towardsthe peripheral area along the radial direction from the central areahaving a large amount of incident light rays. More specifically, fromthe central area of the optical device towards the peripheral areathereof, the topside and the bottom side of the waveguides 112 to 112 fare gradually increased, and the sidewall gradient thereof is graduallydecreased. Thus, in FIG. 16, the rightmost waveguide 112 a correspondingto the center of the optical device has the smallest size, and theleftmost waveguide 11 f corresponding to the outermost area of theoptical device has the largest size.

Furthermore, the spacing between the waveguides 112 may vary to adjustlight distribution. Between the waveguides 112 is formed a valley-likespace, in which a resin 114 having a low reaction index is filled. Thelow index resin 114 may include vinyl silicone, hydride containingsilicone, or the like. The refraction index of the waveguide 112 islarger h at of the low index resin 114, but the smaller the differencein their refraction indices the better. For example, it is preferablethat the refraction index of the waveguide 112 is 1.3˜2.0, and that ofthe resin 114 is no more than 1.3. Of course, if the waveguide has ahigher refraction index beyond the above range, the refraction index ofthe resin 114 becomes higher by as much. As illustrated in FIG. 17, thelow index resin 114 may contain a light diffuser 116 for generatinglight diffusion. That is, in the case where a large amount of light raysare incident through the gap between the bottom sides of the waveguides112 a to 112 f, preferably a light diffuser 116 is added to the lowindex resin 114 to allow the light to be diffused thereinside. In thisway, the light diffuser 116 is used so that the light introduced outsidethe waveguide can be prevented from being lost and a more uniform lightdistribution can be achieved. The light diffuser 116 may be comprised oflight transmissive fine spherical particles.

On the other hand, instead of the light diffuser, the low index resin114 may be mixed with a light-absorbing material (not shown) as in theprevious embodiment. The light-absorbing material may be added, in thecase where the amount of light introduced between the bottom sides ofthe waveguides is small to the extent that it does not affect the entirelight quantity, or whenever required for other purposes. Thelight-absorbing material absorbs light rays incident from the outside ofthe optical device so that the imaging light projected from the insidecan be viewed more clearly and distinctly. The light absorbing materialis formed of a mixture of a monarch-carbon black, a baysilone-platinumcatalyst, and a vinyl silicone material. Optical devices such asprojection TVs and rear projector screens employ the light-absorbingmaterial.

FIG. 18 is a process diagram explaining a method of fabricating theoptical device according to the second embodiment of the invention,which is illustrated in FIGS. 14 to 16. FIG. 19 is a plan view showingthe grid structure of a photomask used in the manufacturing process ofFIG. 18.

As illustrated in FIG. 19, a photopolymer 140 is coated on a photomask130 having a grid structure, in which the line spacing is not uniform(I). As the photopolymer 140, an acrylic synthetic resin is preferred,which can be obtained, for example, by mixing ethoxylated (3) bisphenolA diacrylate, trimethyloloptopane triacrylate, methyl methacylate,n-butyl acrylate, 2-ethylhexyl acrylate, isodecyl acrylate,2-hydroxyethyl acrylate with, as an additive, benzidimethyl ketal,alpha, alpha.-diethyloxy acetophenone, or the like.

Thereafter, ultraviolet rays are radiated on the photopolymer 140 frombelow the photomask 130. At this time, the ultraviolet rays are made toreach the front face of the photopolymer 140. For this purpose, ofcourse, the thickness of the photopolymer 140 coated on the photomask130 should be appropriately controlled. According to the light exposure,the photopolymer 140 is formed with waveguides 112 having non-uniformsize, due to the photomask 130 having a non-uniform grid structure (II).In this embodiment, the waveguides 112 formed above have a uniformheight, but have different sizes, i.e., different bottom and top facesand different sidewall gradients. In particular, the size of thewaveguide 112 is gradually increased, but the sidewall gradient isgradually decreased towards the peripheral area of the optical devicefrom the central area thereof. In FIG. 18, the right-hand siderepresents the central area of the optical device, and the left-handside corresponds to the peripheral area of the optical device. Inaddition, the waveguides placed at the same distance from the centralarea have the same size and the same sidewall gradient.

After the light exposure, the remaining portions of the photopolymer 140other than the waveguides 112 are developed and removed (III). Then, avalley-like space is formed between the waveguides 112. In thesubsequent process step, the space is fined with a resin 114 having alow refraction index (IV). Of course, the resin 114 has a refractionindex lower than that of the photopolymer. A light diffuser may be addedto the low index resin 114.

As shown in FIGS. 1 and 5, in the optical display device 110 fabricatedthrough the above process steps, the waveguides 112 a to 112 f have auniform height. The size of the waveguides is gradually increasedradially towards the peripheral area of the optical device 110 from thecentral area thereof. As described above, since the size of thewaveguides 112 a to 112 f increases gradually and the sidewall gradientthereof decreases gradually toward the peripheral area, thetransmissivity in the peripheral area of the optical device 110, whichis far from the light source and thus has a smaller light quantityand/or a smaller incident angle, is improved, thus creating uniformityin the light distribution over the optical device.

Hereafter, the operation and effect of the invention will be explainedin detail.

FIGS. 20 and 21 show the construction and characteristics of aconventional display device contrasting with the present invention. FIG.20 shows a display panel such as an LCD or an LED, and FIG. 21 is agraph showing the luminance for every section of the display panel ofFIG. 20. FIGS. 22 and 23 illustrate the operational effects of the abovesecond embodiment. FIG. 22 illustrates a display panel having an opticaldevice of the invention mounted thereon, and FIG. 23 is a graph showingthe luminance for every section of the display panel of FIG. 22.

In the conventional display panel 150 where the optical device 10 of theinvention is not mounted, as shown in FIG. 21, the luminancedistribution is not uniform, i.e., the luminance value is highest in thecentral area of each pixel and decreases rapidly in the boundary areasbetween the pixels. In such conventional display devices, non-uniformlights are emitted from each section of the device, thus degrading thehomogeneity in the image quality.

In contrast, as depicted in FIG. 22, in the case where the opticaldevice 110 is mounted on the front face of the conventional displaydevice 150 of FIG. 20, since the optical device 110 of the inventionadjusts the light quantity over the whole area, the central area of thepixels and the boundary area in-between have a uniform luminance, as canbe seen from FIG. 23. Thus, it can be seen that the image generatedthrough the optical device 110 of the invention has a homogenizedquality.

FIG. 24 shows a conventional optical device using a plurality of unitlight sources, and FIG. 25 shows an optical device of the inventionusing a plurality of unit light sources.

As shown in FIG. 24, the light rays emitted from the unit light source160 are very non-uniform, and the luminance thereof is very weak in theboundary area between the unit light sources. In contrast, in theoptical device 110 of the invention, the light rays emitted from theunit light source 160 exhibit a uniform luminance over the entiredevice, as shown in FIG. 25.

In addition, FIG. 26 depicts a conventional display device using asingle diffusion light source, and FIG. 27 illustrates an opticaldisplay device of the invention using a single light source.

In FIG. 26, the light rays emitted from a diffusion light source 170pass through a Fresnel lens and are then projected through a diffusionplate 174, which is formed of uniform-sized waveguides. It can be seenfrom FIG. 26 that the luminance thereof is significantly decreasedfurther away from the light source.

In contrast, as can be seen from the graph of FIG. 27, when the opticaldevice 110 of the invention is employed, the luminance thereof is almostthe same over the entire device, regardless of the distance from thelight source 170. Thus, through the optical device of (be invention, auniform luminance can be achieved, and consequently the homogeneity ofprojected image can be improved.

FIG. 28 is a graph contrasting the light characteristics of the opticaldevice of the invention in FIG. 21 with the conventional one of FIG. 20.In the graph of FIG. 28, the solid line represents the lightcharacteristics of the invention, and the dotted line represents theconventional case. According to the invention, the display device canobtain great uniformity in luminance over We entire section thereof,i.e., the non-uniform light distribution (the dotted line) can betransformed into a uniform state (the solid line).

FIGS. 29 and 30 are a front and rear perspective view of an opticaldisplay device producing a uniform light distribution according to athird embodiment of the invention. FIG. 31 is a sectional view ten alongthe line F-F in FIG. 29. This embodiment illustrates a case ofwaveguides having non-uniform heights.

In this embodiment, the height of the waveguides 112′ in the opticaldevice 110′ is not uniform, but increases gradually towards theperipheral area of the device from the central area thereof. Morespecifically, as shown in FIG. 31, the height of the peripheralwaveguide 112 f in the optical device 110′ is higher than that of thecentral waveguide 112 a′, in such a manner that the peripheralwaveguides surround the central waveguides. The sidewall gradient isalmost the same in all the waveguides 112′. The bottom side and thetopside of the waveguides 112′ are gradually increased the farther awaythey are from the center of the optical device 110′. Consequently, thesize of the waveguides 112′ increases gradually towards the peripheralarea of the optical device 110′.

In addition, a resin 114′ having a low refraction index is filled in thespaces formed between the waveguides 112′. The low index resin 114 hasthe same composition as in the previous embodiment, and in thisembodiment the lower height waveguides 112 a′ to 112 e′ are embedded inthe low index resin 114, as shown in FIG. 31. Therefore, in the centralarea of the device, the light rays are projected through the low indexresin 114′ after passing through the waveguides 112 a′ to 112 e′. In theoutermost waveguide 112 f, its top surface is exposed so that the lightrays are projected directly outward from the waveguide 112. Accordingly,since a relatively intense light is inputted into the central area and arelatively weak light is inputted into the peripheral area, the lightintensity outputted from the optical device 110′ of me invention comesto have a uniform light intensity (luminance).

FIG. 32 is a partial sectional view of another embodiment modified fromthat of FIG. 31. As shown in FIG. 32, a light diffuser 116′ may be addedto the low index resin 114′, which is filled between the waveguides 112a′ to 112 f′. The light diffuser 116′ is mixed with the low index resin114′ in a liquid state and then the mixture of the light diffuser andthe resin is filled between the waveguides 112 a′ to 112 f′. Thecomposition of the mixture is preferred to be 70˜80 wt % of the resin114′ and 20˜30 wt % of the light diffuser 116′. The light diffuser 116′is formed of light transmissive fine spherical particles, the material,particle size and content of which can be controlled to adjust the lightdistribution. The light distribution is adjusted mainly by controllingthe size and height of the waveguides 112 a′ to 112 f′, and the lightdiffuser 116′ serves as an auxiliary means for controlling the lightdistribution.

FIG. 33 is a process diagram explaining a method of fabricating anoptical device according to the third embodiment of the invention andillustrated in FIGS. 29 to 31.

A photopolymer 140′ is coated on a photomask 130′ (i). The coatedphotopolymer 140′ layer has a higher thickness relative to the secondembodiment. At this time, the photomask 130′ has a grid structure whoseline spacing is not uniform. Then, ultraviolet (UV) rays are radiated onthe photopolymer 140′ from below the phoonask 130′. At this time, theultraviolet rays reach the front face of the photopolymer 140′ at theoutermost area thereof, but do not reach the front face of thephotopolymer 140′ at the remaining area. Specifically, towards thecentral area of the optical device, the reaching point is farther awayfrom the front nice of the photopolymer 140′. Then, due to the grid 132′of non-uniform spacing in the photomask 130′, the waveguides 112′ formedin the photopolymer 140′ have a non-uniform size (ii). That is, sincethe grid 132′ spacing increases towards the outer area from the centralarea (from the right hand side to the left hand side in the figure), theformed waveguides 112 have different bottom sides and top sides, i.e., agradually increasing height towards the peripheral area. At this time,the sidewall gradient of the waveguide may be formed to be the same ordifferent.

After the light exposure, the remaining portion in the photopolymer 140′except for the waveguides 112′ is developed and removed (iii). Then, avalley-like space is formed between the waveguides 112′. In thesubsequent process step, the space is filled with a resin 114′ having alow refraction index (iv). The low index resin 114′ covers thewaveguides except the outermost waveguide 112′ in such a way that thesurface of the low index resin 114 is aligned with the light outputsurface of the outermost waveguide. Of course, the resin 114′ has arefraction index lower man that of the photopolymer 140′. A lightdiffuser (not shown) may be added to the low index resin 114′.

As depicted in FIGS. 29 to 31, the optical display device 110′fabricated as described above is structured in such a manner that theheight and size of the waveguides 112′ to 112 f is increased graduallytoward the radially peripheral area of the optical device 110′ from thecentral area thereof. In this way, since the waveguides have an inc gheight and size towards the outer area, the transmissivity in theperipheral area of the optical device 110′, which is far from the lightsource and thus has a smaller light quantity and/or a smaller incidentangle, is improved, thus providing uniformity in the distribution oflight over the optical device.

FIG. 34 is a partial sectional view of an optical display deviceproducing a uniform light distribution according to a fourth embodimentof the invention. FIGS. 35 and 36 explain a method of fabricating theoptical display device of FIG. 34, more specifically, FIGS. 35 and 36are a perspective view and a plan view showing a photopolymer coatingmethod.

As shown in FIG. 34, the waveguides 112 g to 112 i of the invention mayhave different refraction indices to adjust the light distributionthereof. Specifically, photopolymer 140 a, 140 b and 140 c havingdifferent region indices are coated on different sections of the opticaldevice, considering the light quantity and/or the incident angle foreach respective section. Then, as in the previous embodiments, throughlight exposure and development, the waveguides 112 g, 112 h, and 112′having different refraction indices respectively are formed. Forexample, as illustrated in FIG. 35, a multi-nozzle coating die 190 canbe used to coat the photopolymers 140 a, 140 b, and 140 c of differentindices on the photomask 130 a while moving the die 190 along thephotomask. In particular, as illustrated in FIG. 36, the photopolymersare coated in such a manner that the refraction index thereof becomesdifferent towards both vertical end areas from the central horizontalline (the highest intensity of light). At this time, it is preferablethat the refraction index is highest in the central horizon area andbecomes lower gradually towards both vertical end portions. For example,the photopolymer 140 a in the central horizontal area has a reactionindex of 1.60, the photopolymer 140 b in the first adjacent horizontalareas has a refraction index of 1.50, and the photopolymer 140 c in thesecond adjacent horizontal areas (the lowest intensity of light) has arefraction index of 1.40. In this way, different photopolymers 140 a,140 b, and 140 c having different refraction indices can be coated ondifferent sections of the optical device, and, through subsequent lightexposure and development procedures, waveguides 112 g, 112 h and 112Ihaving different refraction indices can be obtained. In this embodiment,the size and height of each waveguide may be made to be the same asshown in FIG. 34, or different for every section as in the previousembodiments. Of course, the low index resin 114 a filled between thewaveguides 112 g, 112 h, 112 i is preferred to be no more than 1.35,i.e., lower than that of the photopolymers 140 a, 140 b and 140 c.

FIGS. 37 and 38 illustrate modifications for the fourth embodiment ofthe invention. FIG. 37 is a plan view of a modification for the fourthembodiment. FIG. 38 is a side view for another modification for thefourth embodiment.

As illustrated in FIG. 37, photopolymers 140 d, 140 e, 140 f, and 140 ghaving different refraction indices are coated on a photomask inconcentric patterns about the center of the optical device. That is, thephotopolymer is coated in such a way that the refraction index thereofis decreased gradually toward radially peripheral areas of the devicefrom the center thereof. Thus, the formed waveguides through subsequentlight exposure and development have a gradually decreasing index towardthe peripheral area in the radial direction, and the waveguides at thesame distance from the center have the same refraction index. Thisconcentric photopolymer coating can be performed by rotating amulti-nozzle coating die 190 a about the center of the optical device.

On the other hand, as illustrated in FIG. 38, the photopolymer may becoated on a photomask 130 b in multiple layers, and the multi-layeredphotopolymer coating 140 h, 140 i and 140 j can be used for providing aspecial function to the optical device.

INDUSTRIAL APPLICABILITY

As described above, in the screen according to the invention, thesidewall gradient of waveguides is made different for each section,depending on the incident angle of imaging light rays inputted into thewaveguides. Thus, the imaging light can be projected at desired angles,for example, in an advertisement board where the viewing angle is ofimportance. In addition, the sidewall gradient of waveguides can becontrolled to adjust the viewing angle, such that only a single viewercan see the screen, excluding other neighboring people. Thus, greatperformance can be achieved, for example, in a surveillance monitorwhere secrecy is of importance.

Furthermore, according to the present invention, in a case where pluralunit light sources are used, the light intensity in the boundary areabetween t light sources can be adjusted to be uniform over all thesections of the display device. In addition, in the case of a singlediffusion light source, the light intensity can be made almost uniformover the central and peripheral areas of the device.

Thus, the optical display device of the invention can be appliedadvantageously to a projection screen, a display for an advertisementboard, or a security screen in order to obtain a distinct, clear andhigh-quality image.

Although the present invention has been described with reference toseveral preferred embodiments, the description is illustrative of theinvention and not to be construed as liming the invention. Variousmodifications and variations may occur to those skilled in the artwithout departing from the scope and spirit of the invention, as definedby the appended claims.

1-39. (canceled)
 40. A display device uniforming light distributionthroughout areas, the optical display device including waveguides eachhaving a sidewall inclined from the bottom side thereof, imaging lightrays incident from a light source placed rearwards of the center of theoptical device being reflected inside the waveguide to be projected tothe outside of the waveguide, wherein the waveguides arranged over thewhole section of a screen have a same bottom side and a same height, andsimultaneously the sidewall gradient in the waveguides is graduallydecreased, within an angle range within which a total reflection occurs,towards the peripheral area of the screen from the central area thereof,such that the imaging light rays are less frequently reflected in thewaveguide in the peripheral area of the screen, as compared with thewaveguides in the central area of the screen.
 41. A display deviceuniforming light distribution throughout areas, the optical displaydevice including waveguides each having a sidewall inclined from thebottom side thereof, imaging light rays incident from a light sourceplaced rearwards of the center of the optical device being reflectedinside the waveguide to be projected to the outside of the waveguide,wherein the waveguides arranged over all sections of a screen have asame bottom side and a same height, and simultaneously the sidewallgradient in the waveguides is gradually decreased, within an angle rangewithin which a total reflection occurs, towards a radially peripheralarea of the screen from the central area thereof, depending on theincident angle, such that the waveguides at a same radial distance fromthe central area have a same sidewall gradient in symmetrical fashionwith respect to the central area.
 42. A display device uniforming lightdistribution throughout areas, the optical display device includingwaveguides each having a sidewall inclined from the bottom side thereof,imaging light rays incident from a light source placed rearwards of thecenter of the optical device being reflected inside the waveguide to beprojected to the outside of the waveguide, wherein the waveguidesarranged over all sections of a screen have a same bottom side and asame height, and simultaneously the sidewall gradient in the waveguidesis decreased gradually, within an angle range within which a totalreflection occurs, along either a horizontal direction or a verticaldirection, towards the peripheral area of the screen from the centralarea thereof, depending on the incident angle.
 43. The optical displaydevice according claim 40, wherein the sidewall gradient of thewaveguide placed in the center of the screen is within a range of 10 to12 with respect to the normal line to a light input surface of thewaveguide.
 44. The optical display device according to claim 40, whereinthe sidewall gradient of the waveguide placed in the peripheral area ofthe screen is within a range of 6 to 8 with respect to the normal lineto a light input surface of the waveguide.
 45. The optical displaydevice according to claim 40, wherein a light-absorbing material isfilled in a space between the waveguides, the light-absorbing materialabsorbing external light flowing into the screen.
 46. The opticaldisplay device according to claim 45, wherein the refraction index ofthe inside of the waveguide is within a range of 1.4-1.6, the refractionindex of the light projection surface of the waveguide is within a rangeof 1.0-1.2, and the refraction index of the light-absorbing material iswithin a range of 1.2-1.3.
 47. The optical display device according toclaim 46, wherein the waveguide is further provided with a diffusionplate at the front face thereof.
 48. The optical display deviceaccording to claim 47, wherein, in a case where the diffusion plate isemployed, the refraction index of the inside of the waveguide is 1.6,the refraction index of the light projection surface is 1.0, and therefraction index of the light-absorbing material is 1.2.
 49. The opticaldisplay device according to claim 46, wherein, in a case where thediffusion plate is not employed, the refraction index of the inside ofthe waveguide is 1.6, the refraction index of the light projectionsurface is 1.1, and the refraction index of the light-absorbing materialis 1.2.
 50. The optical display device according to claim 47, whereinthe critical angle for total reflection inside the waveguide is within arange of 48-70° and the critical angle of total reflection on the lightprojection surface of the waveguide is within a range of 35-60°
 51. Theoptical display device according to claim 50, wherein, in a case wherethe diffusion plate is employed, the critical angle for total reflectioninside the waveguide is within a range of 45-50° and the critical angleof total reflection on the light projection surface of the waveguide iswithin a range of 40-45′.
 52. The optical display device according toclaim 46, wherein, in a case where the diffusion plate is not employed,the critical angle for total reflection inside the waveguide is within arange of 45-50° and the critical angle of total reflection on the lightprojection surface of the waveguide is within a range of 35-40°
 53. Theoptical display device according to claim 40, wherein the opticaldisplay device is applied to a projection screen, an advertisement boarddisplay, and a security screen.
 54. A method for manufacturing anoptical display device according to claim 3, the method comprising: (a)a first step of placing a grid on a photomask and attaching atransparent substrate on the grid; (b) a second step of coating aphotopolymer material on the transparent substrate; (c) a third step ofradiating ultraviolet rays in a line-scanning mode on the photopolymermaterial from below the photomask, the exposure time of ultraviolet raysbeing controlled for each section of a screen so as to form waveguideshaving a sidewall gradient decreasing gradually towards the peripheralarea along one direction from the central area of the screen; and (d) afourth step of attaching a front transparent plate on the waveguides.55. The method according to claim 54, wherein the first step includesthe step of filling a high purity alcohol (IPA) into a gap between thephotomask and the transparent substrate in order to fill a creviceformed by the grid.
 56. The method according to claim 54, wherein theexposure time is configured in such a way as to be shortened in thecentral area of the screen and extended gradually toward the peripheralarea thereof, so that the sidewall gradient of the waveguides decreasesgradually towards the peripheral area of the screen.
 57. The methodaccording to claim 54, wherein the third step includes the steps of:radiating ultraviolet rays on the photopolymer material from below thephotomask to thereby form the shape of waveguides, and developing andremoving the photopolymer material excepting the polymerized waveguideportion.
 58. The method according to claim 54, wherein the fourth stepfurther includes the step of filling a light-absorbing material in aspace between the waveguides, before attaching the front transparentplate.
 59. The method according to claim 54, wherein the transparentsubstrate and the front transparent plate are formed of polyethyleneterephthalate (PET), polymethyl methacrylate (PMMA), or methylmethacrylate (MS) styrene copolymer.
 60. A display device uniforminglight distribution throughout areas, the optical display device havingwaveguides arranged in vertical and horizontal directions, the waveguidehaving a conical shape whose cross-section decreases towards thelight-projection side thereof, wherein at least one of the size, height,spacing, and refraction index of the waveguide is designed to bedifferent for each section, depending on incident angle and/or intensityof light inputted from a light source such that the intensity ofprojected light can be made uniform over all sections of the opticaldevice.
 61. A display device uniforming light distribution throughoutareas, the optical display device having waveguides arranged in verticaland horizontal directions, the waveguide having a conical shape whosecross-section decreases towards the light-projection side thereof,wherein the size of the waveguide is designed to be different for eachsection, depending on incident angle and/or intensity of light inputtedfrom a light source such that intensity of projected light can be madeuniform over all sections of the optical device.
 62. The optical displaydevice according to claim 61, wherein the waveguides arranged in thecentral area near the light source of the optical device have a smallersize and the size of the waveguides increases gradually towards theperipheral area from the central area.
 63. The optical display deviceaccording to claim 61, wherein the height of the waveguides is uniformover all sections of the optical device.
 64. The optical display deviceaccording to claim 61, wherein the height of the waveguide is designedto be different for each section, depending on incident angle and/orintensity of light inputted from the light source.
 65. The opticaldisplay device according to claim 62, wherein a low index resin having arefraction index lower than that of the waveguide is filled in a spacebetween the waveguides.
 66. The optical display device according toclaim 65, wherein a light diffuser is added to the low index resin. 67.The optical display device according to claim 66, wherein the lightdiffuser is formed of light-transmissive spherical fine particles, ofwhich material, particle size, and contents are controlled to adjustlight distribution.
 68. The optical display device according to claim65, wherein a light-absorbing material is added to the low index resin.69. A display device uniforming light distribution throughout areas, theoptical display device having waveguides arranged in vertical andhorizontal directions, the waveguide having a conical shape whosecross-section decreases towards the light-projection side thereof,wherein the refraction index of the waveguide is designed to bedifferent for each section, depending on an incident angle and/orintensity of light inputted from a light source such that the intensityof projected light can be made uniform over all sections of the opticaldevice.
 70. The optical display device according to claim 69, whereinthe refraction index of the waveguides decreases gradually towards theperipheral area of the optical device from the central area thereof nearthe light source.
 71. A method for manufacturing an optical displaydevice, the optical display device having different-sized waveguides fordifferent sections, the method comprising the steps of: (a) attaching aphotopolymer on a photomask having a grid structure whose line spacingis non-uniform; (b) radiating ultraviolet rays on the photopolymer fromoutside of the photomask such that waveguides having different sizes areformed in the photopolymer due to the non-uniform line spacing of thegrid structure of the photomask; (c) removing the photopolymer exceptingthe formed waveguide portions through a development process; and (d)filling a resin having a low refraction index in a valley-like spacebetween the waveguides formed through the development process.
 72. Themethod according to claim 71, wherein, in the ultraviolet rays radiatingstep, the ultraviolet rays are radiated in such a way that they reachthe front face of the photopolymer over the entire region thereof, sothat waveguides having a substantially same height can be formed. 73.The method according to claim 71, wherein, in the ultraviolet raysradiating step, the ultraviolet rays are radiated in such a way thatthey reach the front face of the photopolymer in the outermost areathereof and, towards the central area thereof, they reach furtherinwards of the front face thereof, so that waveguides having differentheights can be formed.
 74. The method according to claim 72, wherein alight diffuser is added to the resin having a low refraction index. 75.The method according to claim 71, wherein, in the photopolymer attachingstep, photopolymers having different refraction indices are coated onthe photomask in a parallel-linear pattern in such a way as to closelycontact each other.
 76. The method according to claim 71, wherein, inthe photopolymer attaching step, photopolymers having differentrefraction indices are coated on the photomask in a concentric pattern.77. The method according to claim 75, wherein the different refractionindices of the photopolymers are decreased gradually towards theperipheral area from the central area.
 78. The method according to claim71, wherein, in the photopolymer attaching step, photopolymers havingdifferent refraction indices are coated on the photomask in a layeredform.
 79. The optical display device according claim 42, wherein thesidewall gradient of the waveguide placed in the center of the screen iswithin a range of 10 to 12 with respect to the normal line to a lightinput surface of the waveguide.
 80. The optical display device accordingto claim 42, wherein the sidewall gradient of the waveguide placed inthe peripheral area of the screen is within a range of 6 to 8 withrespect to the normal line to a light input surface of the waveguide.81. The optical display device according to claim 42, wherein alight-absorbing material is filled in a space between the waveguides,the light-absorbing material absorbing external light flowing into thescreen.
 82. The optical display device according to claim 42, whereinthe optical display device is applied to a projection screen, anadvertisement board display, and a security screen.
 83. The methodaccording to claim 34, wherein a light diffuser is added to the resinhaving a low refraction index.